Paint-removing method

ABSTRACT

A method for removing paint from metal surfaces by boiling a solvent or solvent mixture and contacting the painted metal surface with the vapors of the solvent or solvent mixture. The solvent may include chlorinated liquid hydrocarbons, hydrogenated aromatic solvents, saturated heterocyclic compounds, surface active agents, imidazole derivatives, alkynyl alcohols, glycol ethers, carboxylic acids, ethanolated alkyl guanidine amine complexes, and aliphatic alcohols.

United States Patent [72] inventors Joseph Cooper;

William James Corbett, both of Cincinnati,

Ohio [21] Appi. No. 817,160 [22] Filed Apr. 17, 1969 [45] Patented Dec. 21,1971 (73] Assignee W. R. Grace 8: Co.

New York, N.Y.

[54] PAINT-REMOVING METHOD 9/1954 Judd 7/1968 Crockett OTHER REFERENCES Schwartz, Perry, Berch, Surface Active Agentsand Detergents, 1958, lnterscience Publishers, New York, pp. 109, 110

Primary Examiner-Morris O. Wolk Assistant Examiner-D. G. Miilman AttorneysEugene M. Bond and Kenneth E. Prince ABSTRACT: A method for removing paint from metal surfaces by boiiing a solvent or solvent mixture and contacting the painted metal surface with the vapors of the solvent or solvent mixture. The solvent may include chlorinated liquid hydrocarbons, hydrogenated aromatic solvents, saturated heterocyclic compounds, surface active agents, imidazole derivatives, alkynyl alcohols, glycol ethers, carboxylic acids, ethanolated alkyl guanidine amine complexes, and aliphatic alcohols.

PAINT-REMOVING METHOD This invention relates to a method for removing paint from metal surfaces by stripping with solvent vapors.

Paint-stripping methods using liquid and paste compositions are well known in the art. Typically, the painted surfaces are immersed into hot alkaline baths for paint removal while in other instances a liquid or paste remover is applied to the painted surfaces and the treated paint is removed mechanically by scraping or the like. With some liquid and paste paint removers, the treated paint can be removed by washing.

Very adherent, durable paints and coatings based upon chemically resistant resins such as vinyl, acrylic, epoxy resins or the like have been developed which present a unique problem for conventional paint removal compositions. Although paint strippers have been developed for these durable paints, they have not proven entirely satisfactory from the standpoint of efficient, rapid, removal of such paints. Typically, these compositions require prolonged periods of treatment for complete stripping. The use of aqueous alkali solutions containing phenolic compounds such as cresylates have been employed as hot tank strippers with little commercial acceptance because of the disposal difficulty associated with phenolics.

It has now been found that by the practice of this invention, a method is provided for removing paint from metal surfaces by treating the paint with a solvent vapor which greatly facilitates paint removal. The present method is especially useful for removal of durable paints such as those based on vinyl, acrylic, or epoxy resins.

This invention, generally stated, involves a method for removing paint from metal surfaces by boiling a solvent or solvent mixture for the paint and contacting a metal surface coated with paint with solvent vapor. 1

In the method of this invention, the paint-stripping solvent or solvent mixture is heated to its boiling point and the painted metal surface is contacted with the vapors. The method is preferably carried out in a closed system to prevent loss of vapors and for safety purposes. An apparatus having the structure of a vapor-degreasing machine may be used for this purpose if desired. The stripping apparatus preferably has a portion of the outside enclosed with cooling coils to provide a continuous refluxing of the solvent vapors. The particular apparatus employed, however, is not critical to the practice of this invention.

The method of this invention may be used for removing paints from a wide variety of metals including ferrous, copper, aluminum and like metals and their alloys. The paints which may be removed by this method include varnishes, enamels, lattices, emulsion coatings and the like. Conventional drying oil base paints, acrylic base paints, epoxy base paints, phenolic base paints, and rubber base paints may also be effectively removed. This method is particularly suitable for removing acrylic and epoxy base paints from ferrous metal surfaces such as steel.

The volatile solvents which may be used in the practice of the present invention include chlorinated liquid hydrocarbons, hydrogenated aromatic solvents, saturated heterocyclic compounds, surface active agents, imidazole derivatives, alkynyl alcohols, glycol ethers, carboxylic acids, ethanolated alkyl guanidine amine complexes, and aliphatic alcohols.

Chlorinated liquid hydrocarbons found useful herein include methylene chloride, trichloroethylene, perchloroethylene, trichlorobenzene, orthodichlorobenzene and the like.

Hydrogenated aromatic solvents found useful herein include tetrahydronaphthalene and the like.

Saturated heterocyclic compounds found useful herein include compounds containing nitrogen, oxygen, or both nitrogen and oxygen in the basic structure such as morpholine, N-methyl morpholine, thiomorpholine, dioxane, tetrahydrofu ran and the like.

Surface active agents found useful herein include alkyl benzene sulfonic acid where the alkyl group includes from about eight to about l8 carbon atoms such as dodecyl benzene sulfonic acid.

I lmidazole derivatives found useful herein include materials ,such as those sold under the trade name Miranol CS, an alkyl(coco) ethyl cycloiminidium l-hydroxy 3-ethanol 2- isopropyl sodium sulfonate; Miranol .18, an alkyl(octoic) ethyl icycloiminidium l-hydroxy, S-ethanol Z-isopropl sodium sulfonate; or the like. "Miranols" are synthetic detergents disclosed in U.S. Pat. Nos. 2,528,378 and 2,773,068 (incorporated herein by I reference) and have the formula N CH:

R( JNR1OX o r RiCOOY wherein R is a hydrocarbon radical having from four to 18 carbons, R is a hydrocarbon radical having from one to four carbons, R,CO is an acyl radical having from one to four carbons, X is H, Na, K, CH,COONa, -CH,COOK or CH,COOH, and Y is H, Na, or K.

Alkynyl alcohols found useful herein are exemplified by 3,5-dimethyl-l-hexyn-3-ol and the like.

Glycol ethers found useful herein include materials such as ethylene glycol monomethyl ether, ethylene glycol monethyl ether, ethylene glycol phenyl ether, propylene glycol methyl I ether, and ethoxytriglycol or the like.

Carboxylic acids found useful herein are those having one to about four carbon atoms and include formic acid, acetic acid, propionic acid, and butyric acid.

Ethanolated alkyl guanidine amine complexes usefully employed herein include materials such as that sold under the trade name Aerosol 61 (an ethylene oxide adduct of octadecyl guanidine-amine complex), or the like.

Aliphatic alcohols found useful herein include alcohols such as methyl isobutyl carbinol and the like.

Mixtures of useful solvents may also prove useful in the practice of the present invention. For example, mixtures of about to about 90 parts by weight morpholine with correspondingly about 90 to about l0 parts by weight of a solvent selected from the group consisting of chlorinated liquid 1 hydrocarbons, hydrogenated aromatic hydrocarbons, glycol ethers and mixtures thereof have been found useful. Mixtures of about 10 to about 90 parts by weight of a chlorinated hydrocarbon selected from the group consisting of methylene chloride and perchlorethylene with correspondingly about 90 to about 10 parts by weight of solvents selected from the 2 group consisting of alkyl benzene sulfonic acids, lower aliphatic alcohols and their glycol ethers, alkynyl alcohols, hydrogenated aromatic hydrocarbons, carboxylic acids containing one to four carbon atoms, imidazole derivatives, ethanolated guanidine amine complexes and mixtures thereof 1 may also prove effective in the practice of the present invention.

The compounds of this invention have been found to give the greatest penetration and stripping properties for acrylic enamels. Almost complete paint removal without any I mechanical treatment has been observed.

in order to further illustrate the present invention, the fol- 1 lowing examples are given wherein all parts are by weight unless otherwise indicated.

the following formula: 70"

This formulation appeared as a clear, amber mixture which EXAMPLE 7 boiled at 104 F. The paint hooks were exposed to vapors of this formulation for about 30 minutes after which time loose accumulated paint was brushed off. The hooks were reex- Ingredients Parts by Weight posed to vapors of this formulation for 15 minutes and about 98 percent of paint accumulation was removed. When hooks Methylene Chloride 63.76 having this accumulation of paint are processed by hot tank al- Formic A id (90%) 1 kaline stripping methods, a period of up to 4 hours is usually Smammdmm? Linear Dodecyl Benzene SuIIomc required for comparable paint removal. Add 6 Perchlorocthylene 1 L25 EXAMPLE 2 Paint hooks having 4-inch long sections coated with hit-inch EXAMPLE 8 thick Jones Dabney polymerized acrylamide paint accumula tion were treated to remove the paint. The hooks were placed over beakers containing a mixture of 50 parts by weight Ingredients Parts by Weight morpholine and 50 parts by weight tetrahy'dronaphthalene. Vapors of this mixture from a solvent boiling temperature of 104 F. were contacted with the accumulated paint The effect fl 0 Orthodichlorobenzene 90 of the vapor penetration was readily evident. After a 60 minute interval. the paint had been 90 percent removed. Usually this accumulation of paint requires 3 to 4 hours for EXAMPLE 9 complete removal by using hot tank alkaline stripping methods.

In redients P tsb W ht EXAMPLES 3-17 The procedure of example 2 was repeated with paint hooks Morpholine l0 having similar paint accumulation thereon. The time of expo- Elhmytritlywl 90 sure varied from 15 to 35 minutes using the following formulations in amounts indicated:

EXAMPLE l0 EXAMPLE 3 lngr In Parts by Weight Ingredients Parts by Weight Mor I00 Methylene Chloride B3 Formic Acid (90%) I0 lmidazoline Surtactantol' example l I 40 EXAMPLE 1 Linear Dodecyl Benzene Sull'onic Acid 0 Ingredients Parts by Weight EXAMPLE 4 Methylene Chloride 90 Methyl-iso-hutyl-carbinol 10 Ingredients Parts by Weight EXAMPLE l2 Methylene Chloride 73 Formic Acid (90%) I0 Linear Dodecyl Benzene Sull'onic A id l Ingredients Parts by Weight Ethylene Glycol Phenyl Ether l0 Methylene Chloride )0 EXAMPLE 5 Tetrahydronaphthalene l0 EXAMPLE 13 Ingredients Parts by Weight Methylene Chloride 80 Ingredients Parts by Weight Formic Acid (90%) I0 Ethylene Glycol Phcnyl Ether 6 Guanidine Amine Complex 4 Mclhylcn chlm'idc 50 S Tctrahydronaphthalene 50 6.

EXAMPLE 6 EXAMPLE l4 Ingredients Parts by Weight Ingredients Parts by Weight Methylene Chloride l0 Formic Acid (90%) ll Methylene Chloride 47.6 Ethylene Glycol Methyl Ether 8 Formic Acid (90%) 48 Tetrahydronaphtbalene 47.6

3.5-Dimethyl-l-l-3-ol I EXAMPLE 15 Ingredients Parts by Weight Methylene Chloride 77.5 Formic Acid (90%) I Linear Dodecyl Benzene Sulfonic Acid 2.5 Tetraphdronaphthalene l0 EXAMPLE 16 Ingredients Parts by Weight Methylene Chloride 38.75 Formic Acid (90%) Linear Dodecyl Benzene Sulfonic Acid L25 Tetrahydronaphthalene 55 EXAMPLE 17 Ingredients Parts by Weight Morpholine 50 Tetrahydronaphthalene 50 In all of the above instances of examples 3-17, 75 percent to 100 percent of the paint accumulation on the hooks was removed.

EXAMPLE 18 Four by 6 inches steel panels having four coats of Pittsburgh Plate Glass Duracor 100 acrylic paint in addition to an epoxy primer were treated to remove the paint accumulation. The steel panels were placed over beakers containing a mixture of 73 parts by weight methylene chloride, parts by weight of 90 percent formic acid, 7 parts by weight of weight linear dodecyl benzene sulfonic acid and 10 parts by weight ethylene glycol phenyl ether. Vapors of this mixture were contacted with the accumulated paint. The effect of the vapor penetration was immediately evident. After an interval of 17 minutes, from 95-98 percent of the paint was removed from the steel panels. Usually this accumulation of paint requires 60 minutes by using the most effective hot tank alkaline stripping methods.

EXAMPLES l9-26 The procedure of example 18 was repeated with steel panels having similar paint accumulation thereon. The time of exposure varied from to 30 minutes using the following formulations in amounts indicated:

EXAM PLE 2 1 ingredients Parts by Weight Perchlorethylene 7 Ethylene Glycol Methyl Ether l0 Methylene Chloride 20 EXAMPLE 22 ingredients Parts by Weight Methylene Chloride B0 Formic Acid (90%) I0 Propylene Glycol l0 EXAM PLE 23 Ingredients Parts by Weight Methylene Chloride 745 Formic Acid (90%) 9.3 Water 3.7 Linear Dodecyl Benzene Sulfonic Acid 7.0 Imidazoline Surfactant of example I 5.5

EXAMPLE 24 Ingredients Parts by Weight Methylene Chloride 60 Formic Acid (90%) 20 Propylene Glycol Methyl Ether 10 Linear Dodecyl Benzene Sulfonic Acid l0 EXAMPLE 25 Ingredients Parts by Weight Methylene Chloride 75 Formic Acid (90%) I0 Propylene Glycol Methyl Ether 8 Linear Dodecyl Benzene Suli'onic Acid 7 EXAM PLE 26 Ingredients Parts by Weight Methylene Chloride 73 Formic Acid (90%) 10 Linear Dodecyl Benzene Sull'onic Acid 7 Ethylene Glycol Phenyl Ether N) In all of the above instances of examples 19-26, percent to 98 percent of the paint accumulation on the panels was removed. EXAMPLE 27 Paint hooks having 4-inch long sections coated with 1/ l6- inch accumulation of Glidden acrylic paint were treated for paint removal. These hooks were placed over beakcrs containing a mixture of 80 parts by weight methylene chloride and 20 parts by weight percent formic acid. Vapors of this mixture were contacted with the accumulated paint. The effect of the 7 8 vapor penetration was readily evident. After a 20 minute in EXAMPLE 32 terval, 8590 percent of the paint accumulation was removed from the metal hooks. Usually, this accumulation of paint requires several hours for comparable paint removal by using by welsh hot tank alkaline stripping methods. 5

Perchloroethylene 90 The procedure of example 27 was repeated with paint hooks having similar paint accumulation thereon. The time of 0 EXAMPLE 33 exposure varied from 20 to 30 minutes using the following formulations in amounts indicated:

Ingredients Parts by Weight EXAMPLE 28 Perchloroethylene 80 Linear Dodecyl Benzene Sulfonic Ingredients Parts by Weight Acid Perchlorethylene 36.4 EXAMPLE 34 Methylene Chloride 36.4 Formic Acid 90% 18.2 20 Linear Dodecyl Benzene Sull'onic Acid 90 Ingredients Parts by Weight Perchloroethylene 50 Ethynxytriglycol S0 EXAMPLE 29 in all of the above instances of examples 3234, 75 percent Ingredients Parts by w=i m to 100 percent of the paint accumulation was removed.

It is understood that the foregoing detailed description is perchlomhylenc 30 given merely by way of illustration and that many variations Methylene Chloride so may be made therein without departing from this invention. Di-tri-isoropanolamine 20 wh i l i d i 1. A method for removing paint from a metal surface which comprises, heating a volatile paint solvent to boiling, said EXAMPLE 30 35 volatile solvent formed of 83 parts by weight methylene chloride, 10 parts by weight of 90 percent formic acid and l g part by weight of an imidazoline surfactant having the follow- Ingredients Parts by Weight ing ula Methylene Chloride so CH: Formic Acid 90% 10 Propylene Glycol Methyl Ether l0 I CnH2r-CN--C2H5OH O CHaCHCHzSOaNa In all of the above instances of examples 28-30, 85 percent 4 to 98 percent of the paint accumulation on the hooks was on removed. 1"

contacting the painted metal surface with vapors of the heated EXAMPLE 3 paint solvent, and thereafter removing at least a substantial v amount of the paint from the metal surface.

Paint hooks having 4-inch long section coated with 4- to 2' The method of claim 1 wherein the volatile solvent incl! accumulation of Ford Automotive Acryllc P further includes 6 parts by weight of linear dodecyl benzene were treated for paint removal. These hooks were placed over lf i acid. beakers Containing a mlxtul'fi of Parts y Weight 3. The method of claim 2 wherein methylene chloride is Perchlomemylene, polychlombenzenew 9 P weigh! present in an amount of 63.76 parts by weight, formic acid is linear dodecyl benzene sulfonic acid, and 18.2 parts by weight present i n amount of 17 parts by weight, the imidazoline Of percent formic acid. Vapors Of this mixture were COl'iurfactant is present in an amount of 6 parts weight the tacted with th acc m a e pain Af minutes, 35-90 said benzene sulfonic acid is present in an amount of 6 parts percent of the paint had been remov h usual time" by weight; and the solvent further includes 1 L25 parts by required for complete stripping of Ford Automotive 1-32 weight of perchloroethylene.

Acrylic paint ranges up to 32 hours by using hot tank alkaline 4. The method of claim 2 wherein methylene chloride is stripping methods. present in an amount of 74.5 parts by weight, formic acid is present in an amount of 9.3 parts by weight, the imidazoline EXAMPLES surfactant is present in an amount of 5.5 parts by weight, the

The procedure of example 31 was repealcd with paint said benzene sulfonic acid is present in an amount of 7 parts hooks having similar paint accumulation thereon. The time of by weghti and the Solvent furthfir mcludes Pans by welsh exposure varies but in all instances was less than 45 minutes wamr' using the following formulations in amounts indicated: 

2. The method of claim 1 wherein the volatile solvent further includes 6 parts by weight of linear dodecyl benzene sulfonic acid.
 3. The method of claim 2 wherein methylene chloride is present in an amount of 63.76 parts by weight, formic acid is present in an amount of 17 parts by weight, the imidazoline surfactant is present in an amount of 6 parts by weight, the said benzene sulfonic acid is present in an amount of 6 parts by weight; and the solvent further includes 11.25 parts by weight of perchloroethylene.
 4. The method of claim 2 wherein methylene chloride is present in an amount of 74.5 parts by weight, formic acid is present in an amount of 9.3 parts by weight, the imidazoline surfactant is present in an amount of 5.5 parts by weight, the said benzene sulfonic acid is present in an amount of 7 parts by weight; and the solvent further includes 3.7 parts by weight water. 